Why is a blue ribbon used to designate first prize?

"The usage came from The Blue Riband, a prize awarded for the fastest crossing of the Atlantic Ocean by passenger liners—and prior to that from Cordon Bleu which referred to the blue ribbon worn by a particular order of knights."

https://en.wikipedia.org/wiki/Blue_ribbon

The blue ribbon is a term used to describe or symbolize something of high quality. The usage came from The Blue Riband, a prize awarded for the fastest crossing of the Atlantic Ocean by passenger liners—and prior to that from Cordon Bleu which referred to the blue ribbon worn by a particular order of knights. The spelling blue riband is still encountered in most English-speaking countries, but in the United States, the term was altered to blue ribbon, and ribbons of this color came to be awarded for first place in certain athletic or other competitive endeavours (such as county and state fairs). It also may be applied to distinguished members of a group or commission who have convened to address a situation or problem; the usual usage is "blue ribbon commission" or "blue-ribbon panel".

https://en.wikipedia.org/wiki/Blue_ribbon

In 1348, King Edward III of England established the Order of the Garter, now considered one of the highest orders in the world. Members of the Order of the Garter were distinguished by wearing a dark blue ribbon on their hip.

https://en.wikipedia.org/wiki/Order_of_the_Garter

Also, in the later part on the nineteenth century, British soldiers who practiced abstinence from alcohol, especially in India, wore a medal on a blue ribbon after the first six years of total abstinence.

Look at medal 2354.

http://www.charlesriley.co.uk/britishmedals.htm